Essentials of Ecology

256 CHAPTER 11 Sustaining Aquatic Biodiversity

Trawler

fishing

Drift-net fishing

Purse-seine fishing

Long line fishing

lines with

hooks

Sonar

Fish farming

in cage Spotter airplane

Deep sea

aquaculture cage

Float Buoy

Fish caught

by gills

Figure 11-7 Major commercial fishing methods used to harvest various marine species. These methods have

become so effective that many fish species have become commercially extinct.

■ CASE STUDY

Industrial Fish Harvesting Methods

Industrial fishing fleets dominate the world’s marine

fishing industry. They use global satellite positioning

equipment, sonar, huge nets and long fishing lines,

spotter planes, and gigantic refrigerated factory ships

that can process and freeze their catches. These fleets

help meet the growing demand for seafood. But crit-

ics say that these highly efficient fleets are vacuuming

the seas, decreasing marine biodiversity, and degrading

important marine ecosystem services. Today 75% of

the world’s commercial fisheries are being fished at or

beyond their estimated sustainable yields, according to

the U.N. Food and Agricultural Organization.

Figure 11-7 shows the major methods used for the

commercial harvesting of various marine fishes and

shellfish. Until the mid-1980s, fishing fleets from de-

veloped countries dominated the ocean catch. Today,

most of these fleets come from developing countries,

especially in Asia.

Let us look at a few of these methods. Trawler fishing

is used to catch fishes and shellfish—especially shrimp,

cod, flounder, and scallops—that live on or near the

ocean floor. It involves dragging a funnel-shaped net

held open at the neck along the ocean bottom. It is

weighted down with chains or metal plates and scrapes

up almost everything that lies on the ocean floor and

often destroys bottom habitats—somewhat like clear-

cutting the ocean floor (Figure 11-3). Newer trawling

nets are large enough to swallow 12 jumbo jet planes

and even larger ones are on the way.

Another method, purse-seine fishing, is used to catch

surface-dwelling species such as tuna, mackerel, ancho-

vies, and herring, which tend to feed in schools near

the surface or in shallow areas. After a spotter plane lo-